1. 7.1a. Contrast axial T1 Wtd MRI7.1b. Contrast coronal T1 Wtd MRI Figure 7.1:An enhancing ring lesion within the left posterior frontal lobe 7.1c. Contrast sagittal T1 Wtd MRI Diagnosis: Pyogenic Abscess Differential diagnosis: Metastasis While abscess can be differentiated from metastasis by MR imaging, appropriate patients clinical history and clinical findings are needed to aid in accurate diagnosis.

2. 7.2a,b,c. Pre-Contrast axial T1 Wtd MRI Figure 7.2:Multiple enhancing ring lesions in a immunocompromised patient 7.2d,e,f. Post-Contrast axial T1 Wtd MRI Diagnosis: Fungal Abscesses Differential diagnosis: Multiple Metastasis While abscess can be differentiated from metastasis by MR imaging, appropriate patients clinical history and clinical findings are needed to aid in accurate diagnosis.

3. Fig 7.3a. T2-weighted images of the brain at just above the level of roof of the lateral ventricles of a young homosexual man. Findings: Areas of T2-weighted hyperintensity within the deep paraventricular white matter (arrows). Horizontal section of the brain revealing abnormal left frontal lobe white matter from demyelinization (arrow). Diagnosis: Human Immunodeficiency Virus (HIV) Encephalopathy A myelin-stained section of the brain specimen reveals severe diffuse myelin pallor (*).

4. Fig. 7.3b. T2-weighted image of the brain at the level of frontal horns of a young homosexual man Findings: Foci of T2-weighted hyperintensity involving the peripheral white matter at or close to cortico-medullary junction (arrows) and left basal ganglia (arrow head). Diagnosis: Progressive Multifocal Leukoencephalopathy

5. Fig 7.3c. Post-contrast axial CT image of the brain at the level of frontal horns/basal ganglia of a young homosexual man. Findings: Enhancing ring lesion (arrow) within the left caudate nucleus. Diagnosis: Primary CNS Lymphoma Coronal brain section reveals a tumor involving the left caudate nucleus (arrows). Photomicrographic show perivascular collections of lymphoma cells

6. Fig 7.3d. Post-contrast axial CT image of the brain at the level of the basal ganglia of a drug addict Findings: Enhancing ring lesion (arrow) within the right caudate nucleus. Diagnosis: CNS Toxoplasmosis Horizontal section of the right hemisphere reveals an irregular necrotic lesion in the right caudate nucleus

7. 7.3e. Pre-Contrast Axial T1 Wtd MRI Fig. 7.3e. T1-weighted image of the brain at the level of frontal horns of a young homosexual man Findings: Focal area of T1 Wtd low signal intensity, capping the right frontal horn. Diagnosis: Cytomegalo Virus Infection.

8. Fig 7.3f. Axial T2 Wtd image of the Brain. Findings: Multiple small areas of increased T2 Wtd signal within both basal ganglia (arrows). Diagnosis: Cryptococcal Meningitis Coronal brain section reveals multiple soap-bubble like lesions in the basal ganglia (arrows). Photo micrograph reveals encapsulated Cryptococcus neoformans with budding forms (arrow).